CH PI INTERACTION IN THE CRYSTAL-STRUCTURE OF ORGANIC-COMPOUNDS - A DATABASE STUDY/

The CH/pi interaction is a weak molecular force occurring between CH g roups and pi-groups. A study was carried out by use of the Cambridge S tructural Database in order to obtain insights into the nature of the CH/pi interaction and to examine its role in the crystal packing. The proportion of organic molecules bearing at least one CH/pi interaction in their crystal structures has been found considerable. The CH hydro gen atoms tend to point toward the center of the aromatic ring. A numb er of short CH/pi distances have been shown in the crystal structures of organic compounds. Moreover, the mean CH/pi distance decreases as t he acidity of the CH group increases. These results suggest that the C H/pi interaction is not simply due to the dispersion force but involve s other types of interactions, which are orientation-dependent and eff ective at wider ranges. It was suggested that the CH/pi interaction co nstitutes one of the important factors in controlling, the crystal pac king of molecules.